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7/14/2009 5:01:47 PM
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UCREFRP
UCREFRP Catalog Number
9530
Author
Nelson, S. M. and D. C. Andersen
Title
Butterfly (Papilionoidea and Hesperioidea) Assemblages Associated with Natural, Exotic, and Restored Riarian Habitats along the Lower Colorado River, USA
USFW Year
1999
USFW - Doc Type
Regulated Rivers
Copyright Material
YES
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490 S.M: NELSON AND D.C. ANDERSEN <br />iterative method but correcting for the first and succeeding axes. Rare taxa (those occurring on only a <br />single occasion) were deleted and data log transformed [ln (X+ 1)] before analysis. To test the validity of <br />the CA pattern, the original data-set was randomly rearranged (n = 10 matrices)- to create a null <br />hypothesis assemblage. If the amount of information contained in the original data-set differs significantly <br />(p 5 0.05, 1-tailed test) from the random data-set, it suggests that the pattern is meaningful (Bloom,-1994). <br />Nectar resources and canopy shading <br />During the 1997 field season, the number of flowers or inflorescences considered nectar sources were <br />estimated during butterfly surveys. Although these counts are not a direct measure of nectar, a linear <br />relationship between amount of nectar and number of inflorescences has been found, and it has been <br />suggested that the effort needed to quantify sugar production adds little additional information (Holl, <br />1995). Sampling took place within a 5 m radius circle at disjunct locations every 15 min during a butterfly <br />survey; 16 samples were collected per site each survey month. One-way ANOVA followed by Tukey's test <br />was used to test for differences in mean transformed [ln (X+ 1)] values between sites during each survey <br />month. <br />We used Lux readings from a handheld light meter (Extech®) to compare shading at the sites. We used <br />the percent of the light value under canopy relative to the value in the open as an index of shading at each <br />site. ~ <br />RESULTS AND DISCUSSION <br />Species richness <br />Both species. richness and total butterfly abundance fluctuated seasonally. Mean species richness (Figure --- <br />3a) tended to :"peak in -June regardless of site age, with highest values .consistently. recorded at BW. <br />Abundance values generally paralleled species richness except for the tamarisk-and some revegetated sites <br />in August; when large numbers of Colias eurytheme [associated with -offsite fields of alfalfa.- (Medicago <br />saliva), a host plant] were present (Figure 3b). All sites showed a marked decline in species richness in <br />1996 relative to earlier years, perhaps reflecting a regionwide drought during winter 1995-1996 (Figure 4). <br />Taxa richness, for example,. from combined March and June samples at Bill Williams was 21, 24, and 15 <br />for 1994, 1995, and 1997, respectively, and only 9 for 1996. Because of consistently low values, we did not <br />include the 1996 richness data in the set used to evaluate the relationship between species richness and site <br />age. <br />We found no evidence that older revegetated sites support a greater richness of butterflies than younger <br />sites. In fact, the correlation between butterfly species richness and site age was negative (Spearman rank <br />correlation coefficient, r = - 0.2483; Figure 5). A statistically significant positive correlation (p < 0.05, <br />1-tailed test) would have been reached only with a coefficient value, r > 0.484 (n = 13) (from Zar, 1984). <br />The lowest richness value for BW (Figure 5) exceeded the highest value found at any other site. Richness <br />values at revegetated sites and the tamarisk site were similar, perhaps because a small amount of mesquite <br />and quailbrush was present at the tamarisk site, a trait typical of tamarisk-dominated areas along the <br />lower Colorado River. A species list by site is presented in Appendix A. <br />Nectar resources <br />Revegetated sites tended to have fewer nectar sources than either BW or Tam (Figure 6), Nectar <br />sources, however, were occasionally numerous at moist Havasu Refuge sites. Nectar sources were most <br />numerous in March and June, and rarest in August and November (Figure 6). Nectar sources were low <br />at all sites in November. Although nectar sources were abundant at both Tam and BW, different types <br />of flowers were involved (Figure 7). Most of the flowers or florets at Tam were from tamarisk, while <br />seepwillow flowers contributed more at BW. Other common nectar plants at the sites included mesquite, <br />Copyright ©1999 John Wiley & Sons, Ltd. Regut. Rivers: Res. Mgml. 15: 485-504 (1999) <br />r <br />
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